Potential of plant growth promoting traits by bacteria isolated from heavy metal contaminated soils

Rhizobacteria can enhance biomass production and heavy metal tolerance of plants under the stress environment. The aim of this study was to collect soil samples from different industrial sites followed by their heavy metal analysis. After performing the ICP-AES analysis of soil samples from seven different sites, bacterial strains were isolated from the soil samples of most polluted (heavy metal) site. Phylogenetic analysis of isolates based on 16S rDNA sequences showed that the isolates belonged to four species: Bacillus thuringiensis, Azotobacter chroococcum, Paenibacillus ehimensis and Pseudomonas pseudoalcaligenes. Plant growth promoting activities; siderophore production, indole acetic acid production, HCN production, and phosphate solubilisation were assayed in vitro, and statistically analysis done by using ANOVA analysis and Tukey's Honestly Significant Difference test (p ≤ 0.05). Plant growth-promoting characteristics of isolated strains were higher compared to the control Pseudomonas fluorescens (NICM 5096). In vitro study was performed to check resistance against two heavy metals of isolates. It was observed that isolated bacterial strains have higher heavy metal resistance as compared to control E. coli (NICM 2563). These isolates may cause pathogenic effects, so to avoid this risk, their antibacterial susceptibility was checked against eight antibiotics. Among the eight antibiotics, Ciprofloxacin-1 has shown higher inhibition against all the isolated bacterial strains.